Amp Tech Thread / Ask a tech Q

[liquidsmoke]

From the Rocktron Velocity 300 manual-

"unbridged"
"150 watts per channel @ 4 ohms
75 watts per channel @ 8 ohms
37.5 watts per channel"

"bridged"
"300 watts @ 8 ohms
170 watts @ 16 ohms"

"These standard ¼" jacks provide outputs for Channel 1 to speaker cabinets. Do not connect these outputs
to a load of less than 4 ohms (or less than 8 ohms in mono-bridged mode). These jacks are used when
using the Velocity 300 in "BRIDGED" mode."



This makes no sense to me at all. If the amp puts out 300 watts total stereo(both channels total) at 4 ohms how can it put out 300 watts bridged at 8? The math seems wrong. Bridged is both channels combined together, no?

Bridged will be the two amps in series. In unbridged mode each output is 4 Ohm with 150 watts of power so you can connect a cab of 4 Ohm to each output and get 150 Watts to each, substitute these for 8 Ohm cabs and the power available halves (according to them, more likely it'd be around 2/3s).

So if you have two 8 ohm cabs, one getting the signal from channel A and one getting the signal from channel B they are each only getting 75 watts BUT if you have them both hooked up to channel A bridged then the amp somehow tries to put out more than 300 watts and overheats because the load is 4 ohms? Where does this mysterious extra power come from for bridged mode? If I am understanding this correctly it seems like a very strange design. Why not allow the amp to put out 300 watts bridged at 4 ohms and 150 watts bridged at 8?

It explicitly says do not hook up less than 8 Ohms to in mono bridged mode so you would not hook up two 8 Ohm cabs in parallel i.e. 4 Ohms. If you hooked them up in series you'd have 16 Ohm so you would get 170 watts between the two cabs. There is no mysterious extra power it can only ever put out 300 watts be that in mono or stereo so you've just fucked up the OT by hooking up two low of a load.

There's no way of allowing the amp to put out 300 watts bridged at 4 ohms as it is still two 150 watt 4 Ohm amps in series which will give you an 8 Ohm minimum load.

Ah okay, sort of makes sense now. Leaning towards a Carvin.

[fallen]

My Epiphone Valve Jr. just suddenly started making popcorn sounds instead of sweet rock sounds the other day.

Dead tube? Cap?

I've had amps make random popping noises every once in a while before but never like this.

Nothing plugged in:

[soundcloud]http://soundcloud.com/fallenshallrise/amp-deth[/soundcloud]

[Mr. Foxen]

Something arcing, could be dud valve, could be a dud solder join, dirty socket. Not many valves to swap about to find if its that. I'd start there, toothbrush and alcohol to clean all the valve bases (interdental toothbrush to clean inside the sockets), then resolder bunch likely candidates on the board. That sounds like a valve to me though. Bash about with a plastic chopstick might tell you a bit more, but it seems fairly regular.

[Pissy]

Anyone know where to source some parts for a SUNN Coliseum 300?  A potentiometer 25K linear (according to the parts list I found on the webs) short shaft PCB mount with detent.  It's the master volume.  Also a PCB mount latching pushbutton with a black rectangular cap.
I have trouble navigating the big electronics suppliers websites. I suppose since I don't rightly know all of the details of the parts I'm after.

[Lumpy]

My Valve Jr. just crapped out as well. Heard static sounds like a dirty pot, then silence. Power tube remained lit, preamp tube was hidden by holder -- I pulled the preamp tube with the idea I would walk it over to the local shop for testing... but maybe I should take the whole amp there?

/wtf

[fallen]

Valve jr's are really cheap Chinese made so you wouldn't expect them to be the most durable. I just hope that it's one of those designs that eats tubes instead of a dead major component that scraps it. 

[VOLVO)))]

Lol, you could replace every component inside a Valve jr. For less than 40 bucks.

[Mr. Foxen]

Being lit only tells you the heater isn't broken in a valve, they can be wrong and still glow. Nasty low bidder valves in them are likelly the problem.

[RacerX]

I swapped the tubes out on mine as soon as I bought it.

Sold it to Music-Go-Round and put the old ones back in, so I've got one used & one new Mullard EL-84 from a matched set if anyone needs 'em. I no longer have an amp that uses them.

[fallen]

It's great to have some people to run ideas past... so I finally got around to opening up the Valve Jr so I could have a look while it was making that popping sound and it's the tube for sure.

The heater lights up orange and then there's a blue/purple glow that fires on and off with the loud popping noise. If you tap the tube it makes the same popping noise.

RacerX I need those tubes so let me know what you want for them.

[RacerX]

It's great to have some people to run ideas past... so I finally got around to opening up the Valve Jr so I could have a look while it was making that popping sound and it's the tube for sure.

The heater lights up orange and then there's a blue/purple glow that fires on and off with the loud popping noise. If you tap the tube it makes the same popping noise.

RacerX I need those tubes so let me know what you want for them.

I dunno, maybe 10 bucks + shipping? I think I paid like 20 for the pair.

The one has probably 80-100 hours on it, & the other has never been used.

[Pissy]

Anyone know where to source some parts for a SUNN Coliseum 300?  A potentiometer 25K linear (according to the parts list I found on the webs) short shaft PCB mount with detent.  It's the master volume.  Also a PCB mount latching pushbutton with a black rectangular cap.
I have trouble navigating the big electronics suppliers websites. I suppose since I don't rightly know all of the details of the parts I'm after.

Here it is.


Also,
Notice that trim pot on the right that says "limit adj." I wonder what happens if it twist that thing!!!

[VOLVO)))]

Anyone got the schematic for an Orange Rockerverb 100? I called them and they hung up on me because I told them the build quality is atrocious on their amps.

[Mr. Foxen]

Some come up on google image search: http://www.orangefieldguide.com/OFG_SCHEM/RV50C_sheet1.jpg

Was this US service call? By all accounts the phone service is pretty good from here, but I've never called them because people tend to not bring me shitty modern Oranges to look at, even though I keep hot glue in stock for them.

[VOLVO)))]

Some come up on google image search: http://www.orangefieldguide.com/OFG_SCHEM/RV50C_sheet1.jpg

Was this US service call? By all accounts the phone service is pretty good from here, but I've never called them because people tend to not bring me shitty modern Oranges to look at, even though I keep hot glue in stock for them.

Yep, the US office can smoke my cock, I'm not paying anyone to fix something that is more than likely something stupid and simple because I'm not a "certified Orange technician" or some shit. I'll figure it out, I've got a guy on it...

[dunwichamps]

Some come up on google image search: http://www.orangefieldguide.com/OFG_SCHEM/RV50C_sheet1.jpg

Was this US service call? By all accounts the phone service is pretty good from here, but I've never called them because people tend to not bring me shitty modern Oranges to look at, even though I keep hot glue in stock for them.

Yep, the US office can smoke my cock, I'm not paying anyone to fix something that is more than likely something stupid and simple because I'm not a "certified Orange technician" or some shit. I'll figure it out, I've got a guy on it...

burn it to the ground, then build a OrMat from its ashes

[The Bandit]

New old amp day.
Montgomery Ward GIM-9011A








Came with about 10 of these:


And the reason I posted here as opposed to new acquisitions:


Any idea where it goes?

Gonna be a hunt the legs mission.

SunnJake finally got to this one.  Says it sounds good but hasn't found where the cap goes.
Since I'm a novice at this stuff, the amp doesn't necessarily need that cap?  I would think most all the components are in an amp for a reason.

[RacerX]

So whatever happened to the cheap bastid that started this thread? Haven't heard a peep outta him for some time now...

[justinhedrick]

So whatever happened to the cheap bastid that started this thread? Haven't heard a peep outta him for some time now...

hemi? i think he has retreated to some sink hole in the middle of illinois to demo some new stoner rock jams . . . methinks, at least.

[Metal and Beer]

My 35 year old Randall s/s has developed a quiet yet obvious 60 Hz hum (it goes away w/ amp volume @ zero)....is this indicative of slowly failing capacitors (or such) ?

[VOLVO)))]

My 35 year old Randall s/s has developed a quiet yet obvious 60 Hz hum (it goes away w/ amp volume @ zero)....is this indicative of slowly failing capacitors (or such) ?

Yup, model and year?

[dunwichamps]

yea recap every 25-30 years

[The Bandit]

Sunnjake, update on the Montgomery Ward?  Required any major repairs?

[VOLVO)))]

It's old and it sounds unique, but works fine, but is noisy because they have lights running off the AC lines.

[Metal and Beer]

Is 24 AWG too light for footpedal applications? 18-22 is called for, but I was thinking of using old ethernet wire, if it's not too thin...